ASCE/SEI Overhead Line Loading Standard: Special ETS 2022 Session

The electrical utility industry has used the National Electric Safety Code (NESC) since its first publication in 1914. This Code has been used for the specification of minimum structural loads to design poles and towers that comprise the overhead power grid as well as the minimum electrical requirements for the safe installation, operation, and maintenance of these systems. However, the NESC has a singular chartered focus on “safety”, implying electrical safety and was never intended as a structural design specification. We know this because the NESC explicitly states in its purpose statements, that the Code is to provide a “...standard of safe practices...”, and “…not intended as a design specification…”. As such, it was never intended to be a Code or Standard to provide structural loading or prescriptive performance for in-service reliability. Minimum safety standards as outlined by NESC or California GO 95 are indeed needed and should be required to be followed. As technical advancements have been made in the science of improving our understanding of meteorological events such as extreme wind, extreme ice, seismic, and flooding has evolved, a concerning structural engineering disconnect is emerging. The latest edition of ASCE Manual of Practice No. 74 Guidelines for Electrical Transmission Line Structure Loading (a non-mandatory guide, ASCE 74) reflects that improved science. The requirements of the latest edition of the NESC (a regulatory Code), is chartered to reflect safety rather than structural reliability. The reality of not having an electrical overhead line structural loading standard for the industry is that a patchwork of various levels of reliability and resiliency is being designed into our overhead lines infrastructure, and in some cases only the NESC is used for design loading criteria. When new multi-regional high voltage transmission lines are developed under the competitive environment we are in today, or when electrical distribution lines are upgraded or new lines installed, those lines can be designed based on a wide variety of structural loading requirements. The result is a wide range of inconsistences in applied structural loadings, which in addition to reliability issues, can potentially shorten the service life and increase the lifecycle costs of the overhead line infrastructure. In consideration of the overall increasing national focus on reliability and resiliency, the American Society of Civil Engineers (ASCE) and its Structural Engineering Institute (SEI) has recently approved the development of a national consensus Overhead Line Loading Standard for electrical transmission and distribution structures. Some of the major topics to be covered are minimum design loads, hazard levels, and intended performance goals for the design of structures supporting overhead electrical power lines. The standard will also address joint-use overhead electrical line structures carrying wired telecommunications infrastructure. This paper will discuss the case made for the development of that Standard.